This paper reports the successful installation of the JET ITER-like Wall and the realisation of its technical objectives. It also presents an overview of the planned experimental programme which has been optimised to exploit the new wall and other JET enhancement in 2011/12. IntroductionThe ITER reference materials [pitts] have been tested in isolation in tokamaks, plasma simulators, ion beams and high heat flux test beds. However, an integrated test demonstrating both acceptable tritium retention, predicted to be one to two orders of magnitude lower than for a carbon wall [roth], and an ability to operate a large high power tokamak within the limits set by these materials has not yet been carried out. The ITER-like Wall now installed in JET by remote handling comprises solid beryllium limiters and a combination of bulk W and Wcoated CFC divertor tiles.Work is also well advanced in defining the 2011/12 JET experimental programme and setting up the teams. A phased approach will be adopted which maximises the scientific output early in the programme on the basic materials and fuel retention questions whilst minimising the risk associated with operation in an all metal machine. However, re-establishing H-modes at similar power levels to those with the carbon walls is a priority for establishing a reference database. The JET upgrades also include an increase in neutral beam heating power, up to 35MW for 20s [ciric], this has led to a requirement that the most critical first wall Be and W components are monitored in real time by an appropriate imaging protection system [Alves, Jouve, Stephen]. In the main chamber, an array of thermocouples has been fitted to unambiguously monitor the bulk temperature of critical tiles. Before this upgrade, only a divertor system was available which proved essential for interpretation of IR data [Eich] and this will be even more the case with an all metal wall due to reflection and uncertain emissivity. Safe expansion of operating space will also be a priority. Experiments will have to be carefully managed if they have the potential to jeopardise interpretation of the long term samples which are planned to be removed in a 2012 intervention. Here the concern is that

High fusion power experiments using DT mixtures in ELM-free H mode and optimized shear regimes in JET are reported. A fusion power of 16.1 MW has been produced in an ELM-free H mode at 4.2 MA/3.6 T. The transient value of the fusion amplification factor was 0.95±0.17, consistent with the high value of nDT(0)τEdiaTi(0) = 8.7 × 1020±20% m-3 s keV, and was maintained for about half an energy confinement time until excessive edge pressure gradients resulted in discharge termination by MHD instabilities. The ratio of DD to DT fusion powers (from separate but otherwise similar discharges) showed the expected factor of 210, validating DD projections of DT performance for similar pressure profiles and good plasma mixture control, which was achieved by loading the vessel walls with the appropriate DT mix. Magnetic fluctuation spectra showed no evidence of Alfvénic instabilities driven by alpha particles, in agreement with theoretical model calculations. Alpha particle heating has been unambiguously observed, its effect being separated successfully from possible isotope effects on energy confinement by varying the tritium concentration in otherwise similar discharges. The scan showed that there was no, or at most a very weak, isotope effect on the energy confinement time. The highest electron temperature was clearly correlated with the maximum alpha particle heating power and the optimum DT mixture; the maximum increase was 1.3±0.23 keV with 1.3 MW of alpha particle heating power, consistent with classical expectations for alpha particle confinement and heating. In the optimized shear regime, clear internal transport barriers were established for the first time in DT, with a power similar to that required in DD. The ion thermal conductivity in the plasma core approached neoclassical levels. Real time power control maintained the plasma core close to limits set by pressure gradient driven MHD instabilities, allowing 8.2 MW of DT fusion power with nDT(0)τEdiaTi(0) ≈ 1021 m-3 s keV, even though full optimization was not possible within the imposed neutron budget. In addition, quasi-steady-state discharges with simultaneous internal and edge transport barriers have been produced with high confinement and a fusion power of up to 7 MW; these double barrier discharges show a great potential for steady state operation. © 1999, Euratom

Analysis of MHD activity in pellet enhanced performance (PEP) pulses is used to determine the position of rational surfaces associated with the safety factor q. This gives evidence for negative shear in the central region of the plasma. The plasma equilibrium calculated from the measured q values yields a Shafranov shift in reasonable agreement with the experimental value of about 0.2 m. The corresponding current profile has two large off-axis maxima in agreement with the bootstrap current calculated from the electron temperature and density measurements. A transport simulation shows that the bootstrap current is driven by the steep density gradient, which results from improved confinement in the plasma core where the shear is negative. During the PEP phase (m,n)=(1,1) fast MHD events are correlated with collapses in the neutron rate. The dominant mode preceding these events usually is n=3, whereas the mode following them is dominantly n=2. Toroidal linear MHD stability calculations assuming a non-monotonic q-profile with an off-axis minimum decreasing from above 1 to below 1 describe this sequence of modes (n=3,1,2), but always give a larger growth rate for the n=1 mode than for the n=2 mode. This large growth rate is due to the high central poloidal beta of 1.5 observed in the PEP pulses. Finally, a rotating (m,n)=(1,1) mode is observed as a hot spot with a ballooning character on the low field side. The hot spot has some of the properties of a 'hot' island consistent with the presence of a region of negative shear

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